Known drilling machines include a frame supported for movement over the ground, and a tower mounted on the frame for movement between a generally horizontal stowed position, and a vertical or angled operating position. A deck is supported by the frame and has a generally horizontal upper surface with an opening through which a drill rod is extendable. A rotary head is movable along the tower and engageable with the drill rod to move the drill rod vertically and to rotate the drill rod.
The rotary head urges the drill rod downwardly to penetrate the ground and to create a drilled hole. Known drilling machines are capable of drilling to depths greater than the height of the tower by connecting multiple drill rods together to create a drill string that is longer than the height of the tower. This is accomplished by drilling a first drill rod into the ground until the rotary head is completely lowered. Next, the rotary head is disconnected from first drill rod and raised to the top of the tower such that a second, upper drill rod can be connected to the rotary head. The second drill rod is then threaded to the first, lower drill rod, and the second drill rod can then be drilled into the ground. Additional drill rods can be added to the drill string in a similar manner until the hole is drilled to the desired depth.
With known drilling methods, the drilling depth that is reachable without requiring the use of multiple drill rods is generally limited by the height of the tower. That is, a single drill rod can only be drilled to a depth corresponding to the distance that is traveled by the rotary head in moving from the top of the tower to the bottom of the tower. If a hole having a depth greater than the travel distance of the rotary head is required, additional drill rods must be utilized. The process of coupling and decoupling multiple drill rods to one another in order to drill to a desired depth adds significant time, cost, and complication to a drilling operation. Furthermore, known methods of coupling and decoupling drill rods, including impact breakout systems and non-impact breakout systems, are often inconsistent and can damage the drill rods and the drilling machine.